The opportunities provided by a comparative oncology program designed to study spontaneously occurring tumors in domestic animals can provide appropriate model systems for meaningful cancer research. Naturally occuring cancers more closely resemble human cancers than do the commonly used transplantable rodent tumors. The use of spontaneous tumors in relating research objectives to practical needs of basic and clinical human cancer research should result in information applicable to testing of and suggestion for prevention and treatment of cancer in man. The core of the concept involves the use of an Animal Tumor Clinic located in the veterinary medical teaching hospital at Colorado State University. The clinic provides animal care and subsequent diagnosis leading to therapy trials and related tumor biology studies. This program utilizes group capabilities for studies of various therapy modalities: radiotherapy, chemotherapy, immunotherapy, surgery and of combined methods. Studies of tumor and normal tissue response or toxicity to variable levels of treatment will be made. The program will embody current concepts and collaborations provided by Colorado's medical community and the overall cancer research community. Along with the core programs outlined, additional protocols will with time be developed for in-depth studies on selected animal tumors. Additionally, new research opportunities which arise as a result of the program will be explored.